1. Technical Field
The present invention is relative to a scan lens and more particularly to an interferometric measurement device with the scan lens for measuring a test object.
2. Description of the Prior Art
Interferometric measuring device is an instrument that uses interference patterns formed by a reference beam and an object beam to establish the contours and depth reflection or scattering intensity information of the object under test. Interferometric measuring devices are widely used to scan electronic circuits, optical masks and human tissues, like the application of an optical coherence tomography. FIG. 1 illustrates a conventional interferometric measuring device 10, which comprises a coherent light source module 11, a collimator 12, a beam splitter 13 (for example, beam-splitting mirror), a lens 14, a reflective mirror 15, and a spectrometer 16. The coherent light source module 11 is adapted to generate a coherent light beam I. The collimator 12 is adapted to make the light rays of the coherent light beam I parallel.
The beam splitter 13 is adapted to split the collimated coherent light beam I, thereby generating a reference beam Ir and an object beam Io, wherein the reference beam Ir is projected onto the reflective mirror 15, and the object beam Io is focused by the lens 14 onto the test object 17. The reference beam Ir will be reflected by the reflective mirror 15 to pass through the beam splitter 13 and then to fall upon the spectrometer 16. The object beam Io will be scattered or reflected by the test object 17 and then reflected by the beam splitter 13 onto the spectrometer 16. After falling upon the spectrometer 16, due to optical path difference, the object beam Io and the reference beam Ir will form interference patterns. Thus, the spectrometer 16 can analyze the interference patterns to estimate the contours and structure of the test object 17.
However, the aforesaid prior art interferometric measuring device 10 has a long optical path, not conducive to reduction of the dimension of the interferometric measuring device 10. Further, the interferometric measuring device 10 can simply uses a coherent light source module 11. If a low coherence light source is used, it can cause dispersion problems and an optical path difference between the reference beam Ir and the object beam Io, leading to measurement errors.